Hyperosmolarity-induced vasopressin expression and intrinsic excitability of supraoptic neurons of adult offspring are changed by early maternal separation

Adverse early life experiences can produce long-lasting changes in neurocircuits. The aim of this study was to investigate the programming effects of early maternal separation on the adult offspring vasopressin system. We hypothesized that subjecting adult rats to 4.5 h of daily maternal separation between postnatal days 1 - 21 will have altered hyperosmolarity-induced Avp expression and the response of supraoptic (SON) neurons to electrical and osmotic stimulation. We measured Avp mRNA and hn-RNA in the SON and in the paraventricular nucleus (PVN) by quantitative PCR, and assessed the intrinsic excitability of magnocellular SON neurons as well as their osmotic responses by the patch-clamp technique. In maternally-separated rats we found that basal and osmolarity-induced Avp mRNA gene expression was upregulated in the SON, whereas osmolarity-induced Avp hn-RNA gene expression was abolished. Similarly, in the PVN of maternally-separated rats the osmolarity-induced Avp mRNA gene expression was blunted. The supraoptic neurons of separated rats also had greater excitability than those of non-separated rats. Our results indicate that early maternal separation has long-term consequences on basal and hyperosmolarity-induced Avp hypothalamic expression as well as on the intrinsic excitability of magnocellular supraoptic neurons.

How does early maternal separation and chronic stress in adult rats affect the immunoreactivity of serotonergic neurons within the dorsal raphe nucleus?

Vulnerability to emotional disorders like depression derives from interactions between early and late environments, including stressful conditions. The serotonin (5HT) system is strongly affected by stress and chronic unpredictable stress can alter the 5HT system. We evaluated the distribution of active serotonergic neurons in the dorsal raphe nucleus (DR) through immunohistochemistry in maternally separated and chronically stressed rats treated with an antidepressant, tianeptine, whose mechanism of action is still under review. Male Wistar rats were subjected to daily maternal separation (MS) for 4.5 h between postnatal days (PND) 1-21, or to animal facility rearing (AFR). Between (PND) days 50-74, rats were exposed to chronic unpredictable stress and were treated daily with tianeptine (10 mg/kg) or vehicle. We found an interaction between the effects of MS and chronic unpredictable stress on Fos-5HT immunoreactive cells at mid-caudal level of the DR. MS-chronically stressed rats showed an increase of Fos-5HT immunoreactive cells compared with AFR-chronically stressed rats. The ventrolateral (DRL/VLPAG) and dorsal (DRD) subdivisions of the DR were significantly more active than the ventral part (DRV). At the rostral level of the DR, tianeptine decreased the number of Fos-5HT cells in DR in the AFR groups, both unstressed and stressed. Overall, our results support the idea of a match in phenotype exhibited when the early and the adult environment correspond.

Differential effects of tianeptine on the dorsal hippocampal volume of rats submitted to maternal separation followed by chronic unpredictable stress in adulthood

Early maternal separation (MS) may produce lasting effects in the dorsal hippocampus (DH) that can change its response to chronic stress in adulthood. Chronic stress affects DH morphology and function, but tianeptine (an anti-depressant) can reverse the stress-induced morphological impairments. Morphologic alterations of hippocampus can affect contextual memory. Therefore, we evaluated the effect of tianeptine in MS and chronically stressed rats on: 1) volume of the DH and its areas using stereology and 2) hippocampal-dependent memory using a fear conditioning test. Male Wistar rats were subjected to daily MS for 4.5 h between postnatal days (PND) 1-21, or to animal facility rearing (AFR). Between (PND) days 50 and 74, rats were exposed to chronic unpredictable stress and were treated daily with tianeptine (10 mg/kg) or vehicle, providing eight groups: AFR-unstressed/vehicle (n = 5 for stereology, n = 18 for fear conditioning test); AFR unstressed/tianeptine (n = 6 and n = 10); AFR-chronic stress/vehicle (n = 6 and n = 14); AFR-chronic stress/tianeptine (n = 6 and n = 10), MS-unstressed/vehicle (n = 5 and n = 19), MS-unstressed/tianeptine (n = 6 and n = 10), MS-chronic stress/vehicle (n = 6 and n = 18), and MS-chronic stress/tianeptine (n = 6 and n = 10). MS-chronic stress/tianeptine rats showed a diminished CA1 area than the corresponding MS-unstressed/tianeptine rats. The combination of stressors produced a freezing response similar to those of the control group during postconditioning. During retrieval, MS led to a diminished freezing response compared to the AFR-unstressed groups. Tianeptine had no effect on freezing behavior. Our results show that tianeptine can affect the CA1 area volume differently depending on the nature and quantity of stressors but cannot alter freezing to context.

Maternal separation in early life modifies anxious behavior and Fos and glucocorticoid receptor expression in limbic neurons after chronic stress in rats: effects of tianeptine

Early-life adversity can lead to long-term consequence persisting into adulthood. Here, we assess the implications of an adverse early environment on vulnerability to stress during adulthood. We hypothesized that the interplay between early and late stress would result in a differential phenotype regarding the number of neurons immunoreactive for glucocorticoid receptor (GR-ir) and neuronal activity as assessed by Fos immunoreactivity (Fos-ir) in brain areas related to stress responses and anxiety-like behavior. We also expected that the antidepressant tianeptine could correct some of the alterations induced in our model. Male Wistar rats were subjected to daily maternal separation (MS) for 4.5 h during the first 3 weeks of life. As adults, the rats were exposed to chronic stress for 24 d and they were treated daily with tianeptine (10 mg/kg intraperitoneal) or vehicle (isotonic saline). Fos-ir was increased by MS in all structures analyzed. Chronic stress reduced Fos-ir in the hippocampus, but increased it in the paraventricular nucleus. Furthermore, chronic stress increased GR-ir in hippocampus (CA1) and amygdala in control non-MS rats. By contrast, when MS and chronic stress were combined, GR-ir was decreased in these structures. Additionally, whereas tianeptine did not affect Fos-ir, it regulated GR-ir in a region-dependent manner, in hippocampus and amygdala opposing in some cases the stress or MS effects. Furthermore, tianeptine reversed the MS- or stress-induced anxious behavior. The interplay between MS and chronic stress observed indicates that MS rats have a modified phenotype, which is expressed when they are challenged by stress in later life.

Effect of maternal separation and chronic stress on hippocampal-dependent memory in young adult rats: evidence for the match-mismatch hypothesis

Adverse experiences early in life may sensitize the hippocampus to subsequent stressors throughout the individual's life. We analyzed in male rats, whether, the interaction between early maternal separation and chronic stress affects: (1) the volume of the dorsal hippocampus, (2) CA1, CA2/3 and dentate gyrus (DG) and (3) hippocampal-dependent memory in adulthood. Male Wistar rats were subjected to daily maternal separation for 4.5 h between postnatal days 1-21. From postnatal day 50, animals were exposed to a chronic unpredictable stress paradigm during 24 days. The volumes of the dorsal hippocampus, their areas or strata did not reveal significant differences between treatments. Non-maternally separated and stressed animals showed poor hippocampal performance in a contextual fear conditioning test, with a significant reduction in freezing behavior during post-conditioning compared with control and maternally separated and stressed animals. Also, memory retrieval 24 h after conditioning was significantly weaker in this group than in control animals. Memory performance in maternally separated and stressed rats was similar to control animals. Our results show an interaction between early environment experiences and chronic variable stress in young adulthood as evidence that early stressful experiences do not necessarily lead to a negative outcome but can help in maintaining brain plasticity and increase fitness when animals reach adulthood.

A double-hit model of stress dysregulation in rats: implications for limbic corticosteroid receptors and anxious behavior under amitriptyline treatment

Adversity during early life can lead to diverging endocrine and behavioral responses to stress in adulthood. In our laboratory, we evaluated the long-term effects of early life adversity and its interaction with chronic stress during adulthood. We propose this as a model of vulnerability to dysregulation of the stress response. We hypothesized that rats subjected to both protocols would show differential expression of corticosteroid receptors measured as number of neurons immunoreactive for glucocorticoid receptors (GR) or mineralocorticoid receptors (MR), in limbic areas related to the control of anxiety-like behavior. We also evaluated the effect of amitriptyline expecting to prevent the outcomes of the model. Male Wistar rats were separated from the mother (MS) for 4.5 h every day for the first 3 weeks of life. From postnatal day 50, rats were subjected to chronic variable stress (CVS) during 24 d (five types of stressor at different times of day). During the stress protocol, the rats were administered amitriptyline (10 mg/kg i.p.) daily. MS evoked lower MR expression in the central amygdaloid nucleus and this was reversed by amitriptyline. Furthermore, CVS increased MR immunoreactivity in the hippocampal area CA2 and increased anxious behavior; both effects were prevented by the antidepressant. When MS was combined with CVS during adulthood, there was a reduction of locomotor activity, with no corrective effect of amitriptyline. The differential effects among groups could mean that MS would promote an alternative phenotype that is expressed when facing CVS (a double hit) later in life.

Long-term effects of maternal separation on chronic stress response suppressed by amitriptyline treatment

Abstract The early-life environment has many long-term effects on mammals. Maternal interaction and early stressful events may affect regulation of the HPA axis during adulthood, leading to differential glucocorticoid secretion in response to stressful situations. These adverse experiences during postnatal development may even sensitize specific neurocircuits to subsequent stressors. Later in life, the overreaction of the HPA axis to stress can constitute a risk factor for metabolic and mental diseases. As tricyclic antidepressants are known to correct glucocorticoid hypersecretion during depression, we treated maternally separated animals with amitriptyline, at a lower dose than habitually used in depression models, to prevent the response to chronic stress during adulthood. Male Wistar rats were separated from the mother for 4.5 h every day for the first 3 weeks of life. From postnatal day 50, animals were subjected to chronic variable stress during 24 d (five types of stressors at different times of day). During the stress, protocol rats were orally administered amitriptyline (5 mg/kg) daily. We observed that maternal separation caused a reduction in plasma ACTH levels (p < 0.05), but evoked hypersecretion of corticosterone (p < 0.05) when it was combined with stress in adulthood. This rise was completely prevented by antidepressant treatment with amitriptyline.

Gender-dependent effects of early maternal separation and variable chronic stress on vasopressinergic activity and glucocorticoid receptor expression in adult rats

The aim of the present study was to investigate the influence of early maternal separation on Fos, arginine vasopressin (AVP) and glucocorticoid receptor (GR) expression in the medial parvocellular portion of the paraventricular hypothalamic nucleus (PaMP), and GR expression in the hippocampus of adult male and female rats subjected to variable chronic stress (VCS). Male and female Wistar rats were isolated 4.5 h daily, during the first 3 weeks of life. At 48 days of age, the rats were exposed to VCS. Nonmaternally separated (NMS) females had a higher number of activated AVP neurons than NMS male rats. Maternally separated (MS) females subjected to VCS also showed a higher number of Fos/AVP double-labeled neurons than males with the same treatment. Males and females subjected to early maternal separation and VCS, compared with the MS animals, showed a decrease in the expression of GR in the PaMP. As regards GR expression in the hippocampus, MS animals subjected to VCS as adults, both males and females, showed an increase in GR expression in the subfields CA1, CA2 and CA3. The increase in AVP-immunoreactive neurons coexpressing Fos in response to stress in females exposed to early maternal separation suggests that perhaps early life stress results in a more reactive neuroendocrine stress response in females. Furthermore, our results demonstrate that the different anatomical levels of the hypothalamic-pituitary-adrenal axis have different roles related to its stress response and support the evidence of regional specificity in GR regulation.

Sexual dimorphism in rats: effects of early maternal separation and variable chronic stress on pituitary‐adrenal axis and behavior

The pituitary-adrenal axis response is gender-dependent, showing lower activity in male rats. Furthermore, males showed low emotional behavior and females high emotionality when exposed to such chronic stress situations. The gender of an animal is a relevant factor in the development of responses to stress. The aim of the present study was to investigate the influence of early maternal separation on the pituitary-adrenal activity and emotional behavior of adult male and female rats subjected to chronic variable stress. Male and female Wistar rats were isolated 4.5 h daily, during the three first weeks of life. At 48 days of age, the rats were exposed to variable chronic stress (five different stressors during 24 days). Non-maternally separated and maternally separated males showed lower levels of ACTH compared to females (p<0.01). In male rats exposed to variable chronic stress, the maternally separated animals showed a diminution in the levels of ACTH and Corticosterone (p<0.05) compared to non-maternally separated rats. In the Open Field test, the maternally separated and non-maternally separated-stressed males showed lower emotional reactivity compared with female rats. This was indicated by increase in ambulation (p<0.05) and decrease in defecation (p<0.05). Male rats subjected to variable chronic stress presented low emotional behavior seen in their lower defecation (p<0.05). Stressed females displayed decreased ambulation (p<0.05) and increased defecation (p<0.05), showing high emotional reactivity after exposure to chronic stress. Maternally separated males showed higher emotionality after the exposure to chronic variable stress. This was indicated by decrease in ambulation (p<0.05), decrease in rearing (p<0.05) and increase in defecation (p<0.05). Thus, maternal separation and variable chronic stress caused long-term gender-dependent alterations in pituitary-adrenal activity and emotional behavior.

Behavioral and hypothalamic‐pituitary‐adrenal responses to anterodorsal thalami nuclei lesions and variable chronic stress in maternally separated rats

In maternally separated rats, variable chronic stress decreased the emotional reactivity and provoked a state of hypoactivity of the hypothalamic-pituitary-adrenal system at 3 months old but increased its activity after the open field test. The anterodorsal thalami nuclei control of the endocrine response under stress conditions was not manifested however its seems activate grooming behavior. The development of behavioral and endocrine response to stress is influenced by early postnatal environment. On the other hand, the anterodorsal thalami nuclei exert an inhibitory influence on the hypothalamic-pituitary-adrenal system under basal and stressful conditions. The aim of this work is to determine the magnitude of behavioral and hypothalamic-pituitary-adrenal responses to variable chronic stress in adult female rats with anterodorsal thalami nuclei lesions, previously isolated for 4.5 h daily during the first 3 weeks of life. The groups were: non-maternally separated sham and lesioned, maternally separated sham and lesioned with variable chronic stress with and without open field test. At 3 months old, under variable chronic stress, maternal separation provoked an increase in ambulation in sham and lesioned animals (P<0.01) but this parameter was not modified by lesion in either non-maternally separated or maternally separated groups. Neither the lesion nor the maternal separation changed the defecation and rearing parameter. Grooming behavior was lower in maternally separated lesioned rats (P<0.05). Under variable chronic stress maternal separation decreased adrenocorticotrophin hormone in comparison with non-maternally separated (P<0.001) and the lesion did not alter this response. Regarding corticosterone concentrations, maternal separation did not affect this hormone under variable chronic stress conditions and after the open field test there was an increase of this in both non-maternally separated and maternally separated sham and lesioned (P<0.001).

Sex differences in rats: Effects of chronic stress on sympathetic system and anxiety

In this study we tested whether periodic maternal deprivation (MD) (4.5 h daily during the first 3 weeks of life) caused chronic changes in anxiety and medullo-adrenal responses to chronic stress in either male or female adult (2.5 months of age) rats, or both. Repeated maternal deprivation had a sex-specific effect on epinephrine (E) and norepinephrine (NE) levels: an increase in both measures was observed only in females. Unpredictable stress did not produce changes on plasma catecholamine levels either in males or females. However, when the females were maternally deprived as well as stressed they showed an increase in plasma NE p < 0.05. On the other hand, non-maternally deprived (NMD), maternally-deprived and stressed males showed high levels of catecholamines compared to females p < 0.001. In the elevated plus maze test, MD-treated males displayed a slight increase in anxiety-related behavior compared with NMD rats. This was indicated by a reduction in the time spent on the open arms, whereas females showed less anxiety, indicated by an increase in the number of entries, and in the time spent on the open arms. After exposure to chronic stress only the females displayed decreased anxiety-related behavior. These results suggest that there are sex-induced effects in emotional reactivity, perception of the stressor and in the evaluation of novel situations. Thus, maternal deprivation and chronic variable stress caused both long-term alterations in sympathetic response and gender-dependent changes in the anxiety index of adult rats.

The role of the anterodorsal thalami nuclei in the regulation of adrenal medullary function, beta-adrenergic cardiac receptors and anxiety responses in maternally deprived rats under stressful conditions

Maternal separation can interfere with growth and development of the brain and represents a significant risk factor for adult psychopathology. In rodents, prolonged separation from the mother affects the behavioral and endocrine responses to stress for the lifetime of the animal. Limbic structures such as the anterodorsal thalamic nuclei (ADTN) play an important role in the control of neuroendocrine and sympathetic-adrenal function. In view of these findings we hypothesized that the function of the ADTN may be affected in an animal model of maternal deprivation. To test this hypothesis female rats were isolated 4.5 h daily, during the first 3 weeks of life and tested as adults. We evaluated plasma epinephrine (E) and norepinephrine (NE), cardiac adrenoreceptors and anxiety responses after maternal deprivation and variable chronic stress (VCS) in ADTN-lesioned rats. Thirty days after ADTN lesion, in non-maternally deprived rats basal plasma NE concentration was greater and cardiac beta-adrenoreceptor density was lower than that in the sham-lesioned group. Maternal deprivation induced a significant increase in basal plasma NE concentration, which was greater in lesioned rats, and cardiac beta-adrenoreceptor density was decreased in lesioned rats. After VCS plasma catecholamine concentration was much greater in non-maternally deprived rats than in maternally-deprived rats; cardiac beta-adrenoreceptor density was decreased by VCS in both maternally-deprived and non-deprived rats, but more so in non-deprived rats, and further decreased by the ADTN lesion. In the plus maze test, the number of open arm entries was greater in the maternally deprived and in the stressed rats. Thus, sympathetic-adrenal medullary activation produced by VCS was much greater in non-deprived rats, and was linked to a down regulation of myocardial beta-adrenoceptors. The ADTN are not responsible for the reduced catecholamine responses to stress in maternally-deprived rats. Maternal deprivation or chronic stress also induced a long term anxiolytic effect, which was also not affected by ADTN lesion.

Periodic maternal deprivation and lesion of anterodorsal thalami nuclei induce alteration on hypophyso adrenal system activity in adult rats

The hypothalamic-pituitary-adrenal (HPA) axis is normally regulated by extrahypothalamic limbic structures, among these, the anterodorsal thalami nuclei (ADTN), which exert an inhibitory influence on HPA, in basal and acute stress conditions in rats. In the present work we have investigated whether neonatal maternal deprivation (MD) produces long-term changes in the ADTN regulation of HPA activity. Maternal deprivation, in female rats, for 4.5 hs daily, during the first 3 weeks of life, produced at 3 months old, a significant decrease in plasma ACTH concentration (p<0.001) and an increase in plasma corticosterone (C) (p<0.001), compared to control non-deprived rats (NMD). Also MD showed higher plasma epinephrine (E) and norepinephrine (NE) levels than NMD rats. The increase of NE (66.6% p<0.001) was higher than that observed in E (19%). After 30 days of ADTN lesion, plasma ACTH values were higher than in sham lesioned rats, in both NMD and MD animals. ACTH response was greater in MD rats. Plasma C, in NMD, was higher, whereas in MD lesioned animals, it was significantly lower than in sham lesioned. In MD rats, lesion produced a significant increase in plasma E and NE (p<0.001), and again, NE increase was higher than E increase. The more accentuated increase of NE than E, suggests sympathetic nervous system hyperactivity. In summary, neonatal maternal deprivation induces long-term alterations on HPA axis sensitivity and medullo adrenal secretion; enhanced sympathetic nervous system activity and, therefore affected the ADTN inhibitory influence on ACTH and adrenal glands secretion.

Influence of anterodorsal thalami nuclei on ACTH release under basal and stressful conditions

Experiments were carried out to evaluate the effect of anterodorsal thalami nuclei (ADTN) lesions on plasma ACTH and corticosterone (C), in unstressed and stressed rats. Thirty days after lesion, basal values of plasma ACTH, plasma and adrenal C were significantly higher than those in sham lesioned rats (p < 0.05: p < 0.05; p < 0.01, respectively). Chronic stress (forced immobilization, 15 min/day, during 12 days) in sham-operated animals produced a significat increase in ACTH (p < 0.05) and plasma C (p < 0.05), and a slight decrease in adrenal C, as compared to unstressed rats. In lesioned stressed rats, plasma ACTH was below that found in unstressed lesioned and in sham-lesioned stressed rats (p < 0.05). Variations of plasma C concentrations of stressed lesioned rats were not significant. The adrenal glands of stressed lesioned rats showed a significantly lower content of C than that in unstressed lesioned rats (p < 0.005). It is concluded that ADTN in rats may play a significant role in regulating the hipophyso-adrenal system.